Git - Deprecate `Repository.refs` property to improve performance

[lszomoru]

• Add new git extension API to query for refs
• Update git extension not to rely on the refs property
• Update 1st party extensions to adopt the new git extension API
• Post announcement of the deprecation to vscode-discussions
• Update code so that the refs property always returns an empty array
• Remove the code to keep the refs property from updateModelState

[lszomoru]

Verification steps:

1. Open a folder/workspace that contains a git repository
2. Open the Output window, and switch to the git output channel
3. Open the Source Control view, and click on the "Refresh" action
   • Confirm that the "Refresh" action produced the following output in the git output channel

     2023-03-13 11:44:14.808 [info] > git config --get commit.template [17ms]
     2023-03-13 11:44:14.812 [info] > git for-each-ref --format=%(refname)%00%(upstream:short)%00%(objectname)%00%(upstream:track)%00%(upstream:remotename)%00%(upstream:remoteref) refs/heads/main refs/remotes/main [20ms]
     2023-03-13 11:44:14.977 [info] > git status -z -uall [164ms]
     

4. Open the command palette and invoke the "Git: Checkout to..." command
   • Confirm that the quick pick widget contains all branches, remote branches, tags
   • Confirm that when opening the quick widget the following output is added to the git output channel

     2023-03-13 11:46:02.340 [info] > git for-each-ref --sort -committerdate --format %(refname) %(objectname) %(*objectname) [61ms]